Field
The present invention relates to an acoustic transducer.
Related Art
As well known, compact capacitor acoustic transducers have been manufactured by using MEMS (Micro Electro Mechanical Systems) (see Japanese Unexamined Patent Publication No. 2011-239324, U.S. Unexamined Patent Application Publication No. 2012/0319217, and Japanese Unexamined Patent Publication No. 2008-301430, for example).
A configuration of an existing general acoustic transducer will be described below with reference to FIG. 15.
As shown, the acoustic transducer has a configuration where a diaphragm 60 serving as a movable electrode is opposed with a gap interposed therebetween to a back plate 70 having a fixed electrode 72 provided in a plate 71 made of an insulating material.
The back plate 70 is provided with a plurality of sound holes 75 through which acoustic vibration passes. Moreover, the back plate 70 is provided with a plurality of stoppers 74 that protrudes from the plate 71 to penetrate the fixed electrode 72 and that is made of the same material as the material for the plate 71.
The stoppers 74 are provided to prevent the diaphragm 60 from adhering to the back plate 70 (fixed electrode 72) at manufacturing and use of the acoustic transducer.
More specifically, in a cleaning process after etching of a sacrifice layer in manufacturing of the acoustic transducer, moisture enters the gap between the diaphragm 60 and the fixed electrode 72. Moreover, during use of the acoustic transducer, moisture of moist air or water may enter the gap between the diaphragm 60 and the fixed electrode 72. Then, the distance between the diaphragm 60 and the fixed electrode 72 in the acoustic transducer is about a few μm, and the diaphragm 60 is thin (typically, about 1 μm) and thus has a weak elastic force (restoring force). For this reason, when moisture enters the gap, the diaphragm 60 is adsorbed to the fixed electrode 72 by a capillary action, surface tension and the like of the moisture having entered, and even after evaporation of the moisture, the diaphragm 60 may not separate from the fixed electrode 72 by an intermolecular force, an interfacial force, and an electrostatic force that work between the diaphragm 60 and the fixed electrode 72.
Moreover, at driving of the acoustic transducer, a voltage is applied between the fixed electrode 72 and the diaphragm 60. When an external impact, an external force such as wind, or a large sound pressure acts on the diaphragm 60 in the state where the voltage is applied between the fixed electrode 72 and the diaphragm 60 and thus the diaphragm 60 is largely displaced to come in contact with the fixed electrode 72, short-circuit may occur to break the acoustic transducer.
The provision of the stoppers 74 can prevent a phenomenon that the diaphragm 60 does not separated from the fixed electrode 72 even after evaporation of moisture (the phenomenon that the diaphragm 60 adheres to the back plate 70) and can prevent short-circuit in the diaphragm 60 and the back plate 70 (fixed electrode 72). For this reason, the stoppers 74 are provided.
Note that, in the acoustic transducer shown in FIG. 15, a substrate 65, the diaphragm 60, and the back plate 70 are aligned in this order, and the stoppers 74 is provided on the back plate 70 side. However, there are also known the acoustic transducer having the substrate 65, the back plate 70, and the diaphragm 60 aligned in this order, and the acoustic transducer having the stoppers 74 provided on the diaphragm 60 side.